Determination of borehole injection profiles



March 27, 1956 4T. J. NowAK DETERMINATION OF BOREHOLE INJECTION PROFILES2 Sheets-Sheet ll Filed Sept. 23, 1952 4 derramar' fum/- March 27, 1956Filed Sept, 25, 1952 T. J. NOWAK 2,739,475

DETERMINATION oF BoREHoLE: INJECTION PROFILES 2 Sheets-Sheet 2 kami/muina/Mr United States Patent DETERMINATION OF BOREHOLE INJECTION PROFILESTheodore J. Nowak, Whittier, Calif., assignor to Union Oil Company ofCalifornia, Los Angeles, Calif., a corporation of California ApplicationSeptember 23, 1952, Serial No. 311,017

6 Claims. (Cl. 73-152) This invention relates to a method for loggingwell bores especially well bores, employed forntheinjectignf uids suchas gases or liquids intiperiiieible underground strata." Particularly,this invention relates to the determination of the absloluteinjectionprofile in the secondary recovery of crude petroleiri""d'thlike.

Fluids are injected into permeable underground formations through aborehole penetrating such formations in several well-known types ofoperation. These operations include the underground storage of gases andsecondary recovery operations in which gases or liquids such as waterare employed to displace other valuable fluids through the permeablestrata into a production well. The thus displaced iluids .are thenrecovered from the latter well usually by conventional pumpingtechniques. The secondary recovery operations are ordinarily resorted toonly when the primary recovery processes, such as ilowing and pumping,have become uneconomical.

In the secondary recovery processes, a plurality of wells are drilledinto and through the permeable subsurface strata containing valuablefluids. These wells are ordinarily spaced in a horizontal plane in aregular geometric pattern. For example, an injection well may besurrounded by 3, 4 or 6 production wells spaced at the corners of atriangle, square or hexagon, respectively. An injection fluid, such asgas or water or other specialized ud, is injected into the injectionwell, passes into and through the various permeable strata penetratedthereby and drives the valuable fluids present in such strata toward thesurrounding production wells. Often the geologic structure of theHuid-containing formations is such that a plurality of permeable strataexists. Each stratum of the plurality may vary in thickness as well asin fluid permeability and thus the injection uid will pass at differentrates into the different strata.

lt is highly important to the proper operation of these secondaryrecovery processes to be able yto ascertain exactly the locatio f eachpermeable stratum accepting fluid from th'we'l bore as well as theratesadt whichfluid,

entersxervgrious strata;

Conventional spinner logs and the like are often used to locate pointsof ingress or egress of iluids in secondary recovery processes. Theselogs are subject to a number of serious problems. `The great majority ofwell bores are provided with casings to support the walls of theborehole. These casings are perforated along the casing length,supposedly opposite a permeable stratum into which uid injection isdesired. Leaks in the casing at points other than the perforatedsections appear in the spinner log as an injection point. Any verticalflow of injection iluid between the casing and the borehole wall whichoccurs after passage of the uid through the perforations and beforeentry into a permeable stratum renders a spinner log inaccurate asregards the true position at which the injection fluid enters thepermeable formation. The spinner log is not subject to this disadvantagein an uncased well bore. However, it is a serious disadvantage in theusual cased injection borehole.

ICC

The present invention is directed to an improved method of logging aborehole into the earths crust and through which fluids are passed forinjection into one or more permeable subsurface strata. The methodpermits the 5 determination of the absolute location or depth and theabsolute thickness of the permeable strata receiving fluid from the boreand in addition permits a determination of theabsolutewratewofiluidflowinw each such stratum. The subsequentdescriptionl will be conducted relative to the logging of an injectionwell through which Water is passed into a permeable petroleum-containingformation to eifect the secondary recoveryof' Vthe crude petroleum. Itshould be understood, however, that the method may likewise be employedfor the determination of injection profiles of gas entering undergroundreservoirs, secondary recovery processes using gas drive or in processesinvolving the injection of any other uids into underground strata.

Two highly important features of the present invention include theability of the method to perform with high accuracy in uncased as wellas in perforated cased boreholes. Another important feature is that themethod permits the distinguishing of the rate of fluid injection intoadjacent permeable strata which have differing iluid permeabilities;that is, strata not separated by irnpermeable strata.

It is a primary object of this invention to provide an improved methodfor logging boreholes. e

A more specific object of this invention is to determine the injecting;-gle in a well bore through which fluids are passedfll penetrated by thebore.

A more specific object is to provide a method for the highly accuratedetermination of the absolute length of a section of a well borethroughout which tluid passes from the bore into an undergroundpermeable stratum as Well as a highly accurate determination of therates tvyzhiclsiichjuidsgenter\@e.perrneablestrata.

One specific application of the present invention is in/j thedetermination of the location of water entry into sub?` surfacepetroleum-containing strata and therelativedis- .tributign of theinjected gtegintoa plurality of. permeable strat.\-*-"" 'l Other objectsand advantages of this invention will become apparent to those skilledin the art as the description thereof proceeds.

Briefly, the method of the present invention involves the accuratetemperaturglgggu@ of an injection Well bore under" variousmoperatingconditions and a comparison of the temperature logs so obtained todetermine the limits of the various permeable strata receiving uid fromthe injection well bore as well as the liitiveminjection fluid In thepresent invention, accurate measurements of the temperatures of thefluid at various depths Within the Well bore are performed. One suchtemperature log is run during steadypstate injection of id. One or moresuch logs'arerun 'after the lnjectionwell iswshut in, e. g., the ow oflluid is stopped and no fluid is"`all6we'd to ilow through the borehole.A comparison of the temperature variations under injection and shut-inconditions permits a determination of the volumetric ow rate ofinjection fluid into the permeable underground strata.

The normal temperature of subsurface strata progressively increases withdepth, often rising to 25W-300 F. at 10,000 foot depths and to highervalues at greater depths. These temperatures are generally in excess ofthe temperatures at which the injection fluid is introduced into theinjection well. Consequently, as the injection proceeds and the uid owsdownwardly through the well bore toward the permeable strata, it isheated and the surrounding strata are cooled to temperatures below the 1jection into permeable underground strata l normal geothermaltemperatures (defined below). When injection is stopped and the well isshut in, the cooled portions of the strata adjacent the well bore andthe stationary fluid therein are reheated by heat flowing radiallyinward by conduction from the uncooled outer reaches of penetratedformations toward the bore axis. The temperatures will eventuallyreassume the normal geothermal temperature gradient if the well is shutin A over a prolonged period.

Ordinarily the temperature of the subsurface rises roughly F. perthousand feet of depth along this geothermal gradient. There are severalways in which the geothermal gradient may be established. In an oilfield in which a great number of wells have previously been drilled, acorrelation of the bottom hole temperatures and depth of as many suchwells as possible may be made. A measurement of the bottom holetemperature just following completion of the well is the most desirablesince thermal disturbances at this point are then at a minimum. Thegeothermal gradient may also be determined by running a highly accuratetemperature log through the bore after the bore has come into thermalequilibrium with the subsurface; that is, after a relatively long periodof non-use during which no fluid flow through the bore has beeneffected. Typical geothermal gradients are shown as curves in Figures2-4.

An accurate determination of the geothermal gradient for the reservoirunder consideration is an important step of the present invention.

One step in the method of this invention is the determination of theinjection temperature gradient through the borehole or at least throughthat part of the borehole embracing the strata receiving fluidtherefrom. This temperature log indicates the changes in temperature ofthe injection fluid as it traverses the borehole. In most cases thefluid, when introduced, is at a higher temperature than the temperatureof the formation through the first few hundred feet of depth of the welland in this region the injection fluid loses heat into the formation andis cooled. However, with increasing depth the normal or geothermaltemperature of the subsurface rises and heat is received by the injectedfluid and it rises in temperature. This heat is conducted radiallyinward toward the borehole axis.

When a permeable stratum deeplltlrejnhsu.fwnd v d'm flow f heat by conduil@ s halt o ra ized by the radial ou d flow of injemm remains unheatedas indicated by constant temperature between the top and the bottom ofthe permeable stratum. From this constant temperature noted in the logwhich is run to determine the injection gradient, the upper and lowerlimits h1 and h2 of a permeable stratum receiving fluid from the wellbore may be accurately located. This is true even though the fluidentering such permeable strata leaves the casing at a point above orbelow the particular stratum and enters the stratum after flowingvertically for some distance between the casing and the borehole Wall.In such a case the constant temperature portion ofthe injection gradientappears opposite the permeable strata receiving the fluid even thoughthat portion of the casing is not perforated. Such injection gradientsare shown as curves 42 in Figures 2 and 3 and curve 60 in Figure 4.

is-o the rapiditm Another step of the improved logging method of thisinvention involves slruttingzin the injection well; that is, terminatingthe flovr'cfjction fluid for a period of time during which Ano fluid isadded or removed from the borehole. During this time one or moreadditional temperature logs of the borehole, or at least that part ofthe borehole which penetrates all the permeable strata, are run todetermine one or more shut-in temperature gradients.

Intervals of as low as a few hours to as high as 30 or 40 days, whenpermissible, may separate the shutting in of the well and the running ofthe log to determine the shut-in gradient. r lQurrinU.. theshut-inperiod, the

,radial outward flow of injection Dtid througlmlpetrmeable"strataisreltrcedcioi andwcoiisequent y 'here' is Y zing effect --@Legent e no al inward flow of heat by conduction through themoussubsurfacTfr/atttzvard the borehole axis, which latter has been reducedin temperature by the prior flow of injection fluid. During thisshit-*in period, therefore, the fluid temperature vyl(imirltl'bglfends vtomrise'l as the nor lali-*inward radialwrow oY heatrproceedsl" Thetemperature of thevinjection fluid within the well bore un er s ut-inconditions tends to rise more slow1`y`t fltliHFfftl-ie borehole than dothe tem eratures o wthe mrmwmm'memme recmmfac ttFtadaUUtWard-f flow hasabsorbed heat from and cooled the permeable strata a relatively greatdistance from the bore axis whereas no such extensive cooling occurs inthe impermeable strata through which no fluid flow occurs. The formationtemperature in the permeable strata at a point any given distance fromthe well is therefore substantially less, due to the cooling influenceof the injection fluid passing therethrough, than the temperature of animpermeable formation directly above or below this point and at the samedistance from the well bore. Thus the flow of heat by conductionradially inward toward the borehole axis is very substantially slower inthe cooled permeable strata into which injection fluid has passed thanopposite the impermeable strata into which no fluid flows. Consequently,the fluid temperatures within the bore opposite the permeable stratarise more slowly after the well is shut in. The curves 50 and 52 inFigures 2 and 3 and curve 62 in Figure 4 are typical shut-in gradients.

From an inspection of the shut-in gradient, confirming evidence of thepresence of a permeable stratum receiving fluid from the well bore isfound in the form of relatively low temperature portions of slow heatingcorresponding to the constant temperature portions of the injectiongradient.

Certain boundary heating effects are noted in the shutin gradient atpoints corresponding to the upper and lower limits of the permeablestrata. These boundary effects are caused by vertical heat flow from thewarmer impermeable strata above and below a given permeable stratum intowhich the injection fluid passes. These boundary effects prevent theformation of sharp temperature changes in the shut-in gradient oppositethe upper and lower limits of the permeable strata and hence, with onepresently discovered exception, the limits of the permeable strata aredetermined from the injection gradient where sharp indications ofconstant injection fluid temperature appear.

The one exception referred to above is found in those cases in which twopermeable strata are encountered side-by-side and not separated by alayer of impermeable rock, the two permeable strata having differentfluid permeabilities. Under such conditions, the shut-in gradient showsa relatively sharp temperature anomaly opposite the point on theborehole axis at which the permeable strata of different permeabilityare in contact. This temperature anomaly is more clearly indicated anddiscussed in connection with Figure 4 and is of great importance sinceno dependable indication of this point is ordinarily obtained from theinjection gradient.

After following the above described steps in obtaining the injectiongradient and one or more shut-in gradients by temperature logging thewell bore, the exact upper and lower limits of the permeable stratareceiving fluid from an injection well bore may be located. In addition,the points at which two immediately adjacent permeable strata ofdiffering fluid permeabilities are in contact may also be determined.The foregoing determinations have been proven accurate whether theborehole is uncased through the permeable interval or is provided with aperforated casing through this interval or is partly cased and partlyuncased. These logging steps permit what might be called a qualitativedetermination of the presence of permeable fluid-receiving strata; thatis, the location of the upper and lower limits of such strata. Theadditional steps by which a quantitative determination of injectionrates are described below.

The geothermal temperature gradient is a smooth curve, the temperaturesrising uniformly with depth from the surface. The injection temperaturegradient is also a fairly smooth curve, with the constant temperatureportions opposite permeable strata receiving uid discussed above. Theshut-in temperature gradient is also a smooth curve except opposite thepermeable strata, the temperatures Ts at any given depth risingregularly with time from the injection value Ti to the normal geothermalvalue Tg. The regular portions of a given shut-in gradient are smooth,but opposite the permeable strata anomalously low temperatures are noteddue to the cooling effect of the radial outward uid ow therein. A simpleextrapolation of the regular portions of the shut-in gradient oppositethe impermeable strata across the temperature anomalies opposite stratareceiving fluid gives the extrapolated equivalent shut-in temperaturesTes which would be expected from the shut-in gradient opposite thepermeable fluid-receiving strata had no radial outward fluid ow takenplace. At a given depth in a permeable stratum the shut-in temperatureanomaly AT is Tos -Ts and is due solely to the cooling effect on thepermeable stratum of fluid injected thereinto from the bore. It isproportional to the rate of such fluid injection into the differentialstratum thickness at the given depth. The integral of AT as a functionof depth h of the permeable strata is proportional to the volumetricrate of fluid injected into the whole stratum prior to shut-in. Thesetemperature gradients and the anomalies referred to are more clearlyshown in Figure 2 decribed below.

The mathematical relationships which are employed in the determinationof the injection profiles from the shut-in temperature anomalies AT andthe permeable strata depth limits h1 and h2 are simple.

At a given depth h in the permeable strata and after a given timefollowing shut-in operation, the temperature anomaly AT is equal to:

AT=VTeSTs (l) or the difference between the expected shutain temperatureTes and the actual shut-in temperature Ts. The change of the value of ATwith depth h through the permeable stratum is readily determined fromthe actual and the extrapolated shut-in gradients referred to above,thus AT is a known function of depth h.

Should extrapolation be difficult, a pseudo expected shut-in temperaturegradient Tes in Figures 3 and 4 may be used instead by drawing a curveparallel to the geothermal gradient in the permeable interval andpassing through the point on the shut-in gradient corresponding to theupper depth limit of the upper permeable stratum. Subtantially the sameresults are obtained.

As indicated above, it has been found that the integral of AT as afunction of the depth of the permeable stratum h is proportional to thevolumetric flow of injection fluid into the stratum. The integratedproduct A is:

h A=fh Ac/[(fmdh (2) and the individual stratum injection rate Q is:

Q=kA (3) wherein k is a proportionality constant. The integrated productA according to Equation 2 is the area between the extrapolatedequivalent shut-in temperatures Tes and the actual shut-in temperaturesTs between the depths of the upper and lower permeable stratum limits h1and h2.

The sum of the integrated products A is equal to:

EA or EA=A1+A2+A3 An (4) The sum of the volumetric injection rates Qinto each permeable stratum equals the fluid injection rate Qo at thewell bore inlet, or:

Q0=Q1+Q2+Q3 Qn (5) Substituting Equations 3 and 4 in Equation 5 thetotal injection rate Q0 is:

The individual volumetric injection rates are then directly calculablefrom Equations 3 and 6 and are equal to:

etc.

The drawings, discussed below, clearly illustrate the varioustemperature gradients discussed above and indicate the anomaloustemperature differences AT between the extrapolated or expected shut-intemperature Tes and the actual logged shut-in temperature Ts oppositethe permeable strata receiving fluid.

The total injection rate Qo multiplied by the ratio of the integratedproduct for a given stratum to the total integrated products for allstrata is equal to the individual injection rate as indicated inEquations 7 and 8.

The temperature logs are ordinarily plotted as depth in feet as ordinateagainst temperature as the abscissa and the integrated temperaturedifference with respect to stratum thickness through each permeablestratum is readily determined for such logs; that is, it is equal to theanomalous area between portions of the equivalent and actual shut-ingradients which lie between the depth limits corresponding to the upperand lower depths of the particular stratum. These temperature gradientsare conveniently recorded automatically on a temperature recorder of themoving chart type, which are well-known and commercially available,wherein the chart moves in position corresponding to the depth in thewell bore of the temperature sensitive device employed to measure theHuid temperatures therein.

The method of the present invention as outlined above and the nature ofthe data obtained and the nature of the various temperature gradientsreferred to above are shown more clearly in the accompanying drawings inwhich:

Figure l is a schematic view in'cross section of an injection wellshowing the method of temperature logging,

Figure 2 indicates the appearance of the geothermal, injection andshut-in gradients obtained in the method of this invention,

Figure 3 is an expanded portion of curves in Figure 2 which are enclosedin the dotted rectangle, and

Figure 4 is an enlarged view showing in detail the temperature dataobtained in logging a permeable stratum containing two adjacentpermeable strata of different permeability.

Referring now more particularly to Figure l, well bore provided withcasing 12 extends from the earths surface 14 down to and through twopermeable strata 16 and 18 separated by an impermeable stratum 20. Thecasing opposite the permeable strata are provided perforations 22 whichpermit the injection of injection fluid into the permeable strata.Injection fluid is introduced at the top of the well through line 24 ata rate controlled by valve 26 and flows down the bore, through theperforations into the permeable strata.

A temperature sensitive device indicated generally at 28 is suspendedwithin well bore 10 by cable 30 which passes upwardly through the top ofthe well bore over sheave 32 and onto cable drum 34. Through slip rings,not shown, temperature recorder instrument 36 is connected to cable 3i).A temperature log is obtained by passing temperature sensitive means 28through the well bore in contact with the injection fluid and thetemperature indications obtained are plotted as a function of positionor depth within the well bore by instrument 36. The temperaturesensitive means may be moved slowly through the well bore or may behalted every few inches or every few feet while the temperature readingis obtained and recorded. The latter method is preferable since a morehighly accurate temperature reading is thereby obtained.

Referring now more particularly to Figure 2, this figure is disposed tothe right of Figure l in such a position that the temperature dataappearing in Figure 2 correspond to the temperatures existing at pointswithin casing 10 horizontally to the left in Figure l. In Figure 2 thelocations of permeable strata 16 and 18 are indicated at the left. Curve40 shows the geothermal gradient normally existing through theundisturbed formations. Curve 42 indicates the injection gradient whichis the variation in temperature of the injection uid, under constantflow rate conditions, with depth through the well bore. As is apparent,the upper portion of curve 42 indicates a drop in temperature which isusual in view of the fact that the injection fluid is generally warmerthan the geothermal temperature just below the surface. The central partof the curve indicates a gradual warming of the injection fluid as itpasses through deeper formations at increasing temperatures. Thatportion of curve 42 indicated generally as 44 is a zone through whichfluid injection into permeable stratum 16 takes place, counteracting thenormal geothermal heating effect and resulting in a constant temperaturefrom the top to the bottom of this stratum. That portion of curve 42indicated generally as 46 appears opposite impermeable stratum in whichthe normal geothermal heating occurs resulting in a slight temperaturerise. That portion of curve 42 opposite permeable stratum 18 isindicated generally as 48 and through which the constant temperaturecharacteristic of fluid loss is noted. The lowest portion of curve 42shows a relatively rapid approach of the fluid temperature toward normalgeothermal temperature at the bottom of the casing where little if anyfluid liows.

Curves 50 and 52 indicate the shut-in temperature gradients afterperiods of 3 and 8 days respectively. In the upper three-quarters ofeach of these curves it is noted that the normal geothermal heatingradially inward in the absence of injection fluid flow down through thebore causes the fluid temperatures within the well bore to rise fromthose of curve 42 and gradually approach the normal geothermal gradientas indicated in the upper threequarter portion of curve 40. However, thepoints opposite permeable strata 16 and 18, into which injection fluidhas been flowing and which has been cooled thereby, it is noted that asubstantially lower degree of heating has taken place due to the factthat these strata have been extensively cooled due to fluid injection.The temperature log therefore obtained in actually determining theseshut-in gradients exhibits a pronounced anomaly in temperature atpositions in the bore corresponding to these permeable strata. Thesetemperature anomalies are indicated by those solid portions of curves 50and 52 opposite permeable strata 16 and 18 and to the left of the shadedareas. Had no permeable strata been present at these points, the shut-ingradients 5'0 and 52 would have included the dotted (extrapolated)portions to the right of the shaded areas. The normal geothermal heatingtakes place opposite impermeable stratum 20 so that those portions ofcurves S0 and 52 opposite this strata indicate the normal approachduring shut-in toward the geothermal temperatures indicated by curve 40.

Referring now to Figure 3, an enlarged view in greater detail of thelower portion of the curves in Figure 2 is shown. The curves andportions thereof are designated in Figure 3 by the same numbers employedin Figure 2. The anomalous difference between Ts and Tes is clearlyshown, this difference being AT referred to in Equation l. Whereasduring 3 days shut-in, the temperature Ti would be expected to rise to avalue of Tes, it only rose to a value TS and the difference AT is ameasure of permeable strata cooling due to the injection fluid owthereinto.

The determination of the location of the upper and lower limits In andh2 of permeable strata 16 and 18 are obtained from the injectiongradient, curve 42. Point a" is determined at the uppermost extremity ofthe straight or constant temperature portion of curve 42 oppositepermeable stratum 16. The lower extremity of permeable strata 16,designated b" is determined where the inflection occurs near the lowerextremity of the constant temperature portion of curve 42 or at thelower end of the sharply curved portion of curve 42. The slightcurvatures above points a" and b" are caused by boundary effectsresulting from vertical flow of heat. These points may be moreaccurately located in curve 42 than in curves or 52 and therefore thedetermination ot the upper and lower extremities In and hz of permeablestratum 16 is made from the injection gradient 42. A horizontal linedrawn through points zz" and b" through the shut-in gradient, curve 50,defines the upper and lower dcpth limits on that gradient. An analogousdetermination of the limits of stratum 18 and any others is made as justdescribed.

The normal geothermal temperatures existing at the depths /11 and h2 forstrata 16 and 18 appear on geothermal gradient 40 as points a, b, c andd. The integrated product A, as defined by Equation 2 given above, forstratum 16 is equal to the area bounded by a', a, b and b which isdesignated as A1 for shut-in gradient 50. In Figure 3, this area is theupper cross-hatched area. The total integrated product 2A is the sum orarea A1 plus the area bounded by c', c", d' and d which is designated asA2 and is the integrated product for stratum 18. This is indicated asthe lower cross-hatched area in Figure 3. The sum of the integratedproducts or areas A1 and A2 is in this example equal to EA, since onlytwo permeable strata receive fluid. According to Equation 7, therefore,the injection rate Q1 into permeable stratum 16 is equal to the totalinjection rate Qo times the ratio of A1 to 23A. Obviously, the analogouscalculation for the determination Q2, the liow rate into stratum 18, isQ0 times the ratio of A2 to EA.

A check determination of the shut-in gradient may be made after 8 days,for example, in which case shut-in curve 52 and extrapolated equivalenttemperatures are employed in the same way. Good agreement is nearlyalways obtained between such check determinations when carefultemperature logging procedures are employed.

Referring now to Figure 4, the nature of the data obtained when twoadjacent permeable strata 64 and 66 are encountered is shown. Thegeothermal gradient again appears as curve 40. The injection gradient isshown as curve 60. A single shut-in gradient is shown as curve 62 andagain the anomalous temperature difference AT between the expectedvalues of Tes and the actual values TS is indicated by a shaded area.The depth limits of permeable stratum 64 are indicated at h1 vedeva andha, the upper and lower limits of adjacent permeable stratum 66 areindicated as h2 and h3. No normal geothermal heating during shut-inwould be expected between the adjacent permeable strata at depth h2 dueto the absence of an impermeable stratum therebetween. However, it hasbeen found that the temperature rises during shut-n operation oppositethese permeability discontinuities causing a higher temperature toappear at point b" corresponding to the line of demarcation between theadjacent strata 64 and 66 at which the permeability changes. This effectis highly important since the injection gradient shows no deflection atpoint b" and thus the depth h2 is determined in this one exceptionalcase from the shut-in gradient 62 opposite the location of point b.

The relative injection rates of strata 64 and 66 are determinedaccording to the procedures outlined above; that is, the integratedproduct for stratum 64 is determined from area A3 bounded by points a',a, b, and b' and the integrated product corresponding to stratum 66 isdetermined from area A4 bounded by points b, b", c" and c'. The sum ofA3+A4 is equal to 2A in Equation 6. The individual injection rates Q3and Q4 are determined by multiplying the total injection rate Q inbarrels per day times the ratio of A3 and A4 respectively to EA asdescribed above.

As an example of the present invention, data are given, below in tabularform, which were obtained during the logging of an injection well,designated as Callender No. 90, located in the Dominguez oil field ofSouthern California. Prior to shutting in the total injection rate Qowas slightly over 990 barrels per day of oil eld brine. The well waslogged to determine. the injection gradient according toV thisinvention. The well was then shut in for a period of 6 days and thenagain logged to determine the shut-in gradient. The permeable stratawere found between depths of 5900 feet and 6365 feet and three principalinjection zones appeared. The shut-in gradient was extrapolated acrossthis interval and the magnitude'of the temperature anomalies AT rangedas high as 20 P. at the 6080 foot depth. The areas A were calculated foreach 20 foot interval. The individual injection rates Q1 in barrels perday for each 20 foot intervaly 'were calculated according to Equation 7and then calculated over to a volume per day per foot of depth basis. Inthe table below column l is the mean depth of theinterval considered,column 2 lists the upper and lower limits h1 and h2 of the interval,column 3 lists the integrated products (see Equation 2) A for eachinterval, and-columns 4 and 5 list the individual injection rates foreach interval and rate per foot of interval respectively. i

Table Injection Rates in Mean Depth Depth Limits Integrated Interval ofInterval, of Interval, Product It. ft. A, sq. in.

B./D. B./D./ft.

5, 910 5. 900-5, 920 0. 122 5. 95 0. 298 5. 930 5. 920-5, 940 0. 317 l5.47 0. 774 5, 950 5, 940-5, 960 0. 44 21. 45 1.073 6, 010 6, OOO-6,020 1. 41 68. 9 3. 445 6, 030 6, O20-6, 040 1. 62 79. 1 3. 955 6, 050 6.040-6, 060 2. 04 99. 6 4. 980 6, 070 6, 060-6, 080 2. 04 99. 6 4. 980 6,090 6, 080-6, 090 1. 82 88. 9 4. 445 6, 270 6, 260-6, 280 1. 76 86. 0 4.30 6, 290 6, 280-6, 300 1. 73 84. 5 4. 225 6, 310 6, 300-6, 320 2. 20107. 5 5. 375 6, 330 6, 320-6, 340 2. 20 107. 5 5. 375 6, 352 6, 340-6,365 2. 58 126. 0 5. 03

The injection profile is obtained by plotting the incremental injectionrate in barrels per day per foot in column 6 of thev table above againstthe depth of the increment. f

The continuous thermometric procedures usually employed to log boresinvolve moving the temperature sensitive element through the bore atvelocities of from 40 to feet per minute. This has been foundunsatisfactory in the method of this invention because the definition ofthe anomalies is lost. As much as a 50 foot error due to the thermal lagof the device has been noted.

A semi-continuous procedure has been found necessary wherein thetemperature sensitive device is lowered at a rate of 500 feet per minuteto a point just above or below the injection interval. At this point thedevice is stopped for a period of at least 10 minutes to attain thermalequilibrium. Then the injection interval is logged by passing the devicethrough the permeable interval in increments of from l to 50 feetdepending upon the thickness of the interval. In California oil sands ofover 100 feet thickness, incremental depths of l0 to 25 feet aresatisfactory while in other thinner sands an increment of 5 feet isemployed. In any interval, the smaller increments give greaterdefinition of the various injection strata.

At each incremental depth the temperature sensitive device is heldstationary for a period of at least 3 minutes to reach local thermalequilibrium, the temperature reading taken and recorded, manually orautomatically, and then the device is moved through the next incrementand the temperature reading repeated. It has been found that injectionintervals of several hundred feet in thickness c an be successfullylogged with high degrees of accuracy in this semi-continuous manner in aperiod of a few hours and that no substantial temperature change occursat a given point during that time.

Another requirement for successful logging to determine the shut-ingradient is that the injection well be shut-in for a certain period toallow all backow in the bore to cease prior to determination of theshut-in gradient. In most cases this period of delay should exceed 5hours and preferably l0 hours or more should elapse. This period willvary with individual well bores.

The accuracy of temperature measurements is preferably as high aspossible, being at least to the nearest 0.5 F. and preferably to thenearest 0.1 F. An Amerada gauge has been found satisfactory when usedaccording to the semi-continuous method described above.

If possible temperature sensitive devices, such as thermocouples,thermopiles or others based on different principles, may be employed ifgreater accuracy may be obtained. Instruments correct to the nearest0.l0 F. or better are highly desirable.

It is to be understood that the foregoing description and illustrationof the method of this invention have involved the injection of a fluidwhich is at a lower ternperature than the underground permeable strataso that the strata are cooled and the fluid is warmed as it passesthrough the borehole. This is not a limitation of this invention becausein cases where heated fluids are injected and pass through the boreholeat temperatures above the normal geothermal temperatures, the fluidswill be cooled and strata are heated. The injection gradient thenappears to the right of the geothermal gradient, the same constanttemperature portions thereof appear opposite permeable fluid receivingstrata, and after shut in the fluids in the bore-hole opposite theimpermeable strata cool more rapidly than uid opposite the permeablestrata which have been extensively heated by the heated injection fluid.Analogous temperature anomalies appear in the shut-in gradients and thesame calculations apply to determine the individual injection rates, e.g. the injection prole.

Further, the method of this invention is applicable to liquid or gaseousinjection fluids because analogous thermal relationships have been foundto apply.

A particular embodiment of the present invention has been hereinabovedescribed in considerable detail by way of illustration. It should beunderstood that various other modifications and adaptations thereof maybe made by those skilled in this particular art without departing fromthe spirit and scope of this invention as set forth in the appendedclaims.

I claim:

l. A method for determining the injection profile of an injectionborehole penetrating an underground interval containing fluid permeablestrata which comprises continuing the injection fluid ow downwardlythrough said borehole and into said strata at a steady rate; measuringthe variation of injection fluid temperature within said borehole duringinjection by lowering a temperature sensitive device to a point adjacentthe permeable strata within said borehole, holding it stationary for atleast 5 minutes, moving said device through successive incrementaldepths opposite said permeable strata, holding said device stationaryfor at least 3 minutes at each incremental depth, recording the fluidtemperature at each depth whereby the temperature variation with depthis established as an injection temperature gradient and whereby theprecise upper and lower depth limits of the permeable strata receivingfluid are established from constant temperature portions of saidinjection gradient; subsequently shutting in the well for a periodsufficient to terminate all back flow therein, then measuring thevariation of the injection'uid temperature within said borehole in theabsence of injection uid flow by the steps as employed to determine saidinjection temperature gradient thereby establishing a shut-intemperature gradient having temperature anomalies therein at depthscorresponding to the permeable strata whereby the area of said anomaliesbounded by the actual and the expected shut-in gradients and bounded bythe upper and lower depth limits for each incremental depth of permeablestratum establishes the injection profile in terms of the incrementalvolumetric injection rate Q for each incremental depth of permeablestratum from:

(wherein Q1 is the incremental injection rate for the first incrementaldepth of permeable stratum, Qu is the total volumetric injection rateinto said borehole, A1 is the incremental area of the temperatureanomaly in the shut-in temperature gradient corresponding to the firstincremental depth of permeable stratum, and EA is the total anomalousarea opposite all of the permeable strata); and continuing the injectionfluid flow into said borehole.

2. A method for determining the injection profile f a well bore throughwhich injection fluids are passed into permeable underground stratapenetrated thereby which comprises determining the injection temperaturegradient within the well bore while continuing the fluid injection,shutting in the well for a period sufficient to terminate all fluid flowtherein, next determining at least one shut-in temperature gradientwithin said bore in the absence of fluid ilow; said gradients beingdetermined by the steps of lowering a temperature sensitive device to apoint adjacent the permeable interval, suspending it at said point toattain thermal equilibrium therein, then passing said device throughsaid well bore opposite the permeable interval, recording the indicatedtemperature of the fluid therein as a function of depth in said bore toestablish said shut-in and injection temperature gradients; and thencontinuing the injection of said injection uid into said well bore; theprecise depths of the upper and lower limits of each permeable stratumbeing established by constant temperature portions in said injectiongradient, said shut-in gradient having anomalous regions through thedepths corresponding to each permeable interval, the injection profilein terms of successive injection rates Q for each incremental depthdifference in a permeable stratum being calculated from:

(wherein Q1 Qn etc. are incremental volumetric injection rates for eachincremental depth difference in a permeable stratum, Qo is the totalfluid injection rate into the well bore and into all the permeablestrata penetrated thereby, A1 An are the anomalous incremental areasbetween said shut-in gradient and the expected shut-in gradientconsisting of an extrapolation of said shut-in gradient through theanomalous temerature regions thereof, said areas being further boundedby the upper and lower depth limits of each incremental depth differencein a permeable stratum, and EA is the total of all the anomalousincremental areas A).

3. A method according to claim 2 in combination with the step ofcontinuously measuring the depth of the points at which saidtemperatures are measured, and recording said temperatures as a functionof depth within the well bore to record said injection and shut-intemperature gradients.

4. A method for determining the injection profile of a well bore throughwhich injection uids are passed into permeable underground stratapenetrated thereby which comprises determining the injection temperaturegradient within the well bore while continuing the fluid injection,shutting in the well for a period of at least 10 hours to terminate alluid ow therein, next determining at least one shut-in temperaturegradient within said bore in the absence of fluid flow; said temperaturegradients being determined by lowering a temperature sensitive device toa point adjacent the permeable interval, suspending it at said point forat least 10 minutes to attain thermal equilibrium, then positioning thedevice successively through the permeable interval at a plurality ofpoints separated by known incremental depth differences, recording theindicated temperature after holding said device stationary at least 3minutes at each successive point, said temperatures being plotted as afunction of depth within said borehole to obtain said shut-in andinjection temperature gradients, and then continuing the injection ofsaid uids; the precise depths of the upper and lower limits of eachindividual permeable stratum receiving fluid being established from theupper and lower limits of constant temperature portions of saidinjection temperature gradient; the injection prole being determinedfrom the incremental in jection rates Q for each incremental thicknessof said permeable strata which in turn are established from:

@FaQ-] ere.

(wherein Q1 Qn etc. are the incremental volumetric injection rates forsaid incremental thicknesses of permeable strata, Qo is the total uidinjection rate into said well bore, A1 An etc. are areas of anomalousregions in said shut-in temperature gradient and which are bounded byshut-in gradient and the expected shutin gradient obtained byextrapolating the shut-in gradient through the anomalous temperatureregion thereof and further bounded by the upper and lower depth limitsof each incremental thickness of the permeable strata, and 2A is thetotal area of the anomalous incremental area A).

5. A method for determining the injection prole of a well bore throughwhich injection fluids are passed into permeable underground stratapenetrated thereby which comprises determining the geothermaltemperature gradient through the permeable interval, determining theinjection temperature gradient within the well bore while continuing thefluid injection, shutting in the well for a period of at least l hoursto terminate all lluid ow therein, next determining at least one shut-intemperature gradient within said bore in the absence of uid ow; saidinjection and shut-in gradients being separately determined by the stepsof lowering a temperature sensitive device through the well bore to apoint adjacent the permeable interval, suspending it at said point forat least minutes to attain thermal equilibrium, then positioning thedevice successively at a plurality of points separatedby incrementaldepth differences opposite the permeable interval penetrated by saidwell bore, recording the temperature indicated at each successive depthpoint after holding said device stationary for at least 3 minutes ateach of said points, and continuing the injection iluid flow into saidwell bore; said injection temperature gradients having anomalous regionsof constant temperature and said shut-in gradients having anomaloustemperature regions thereon corresponding to the depths of eachpermeable stratum, the precise depths of the upper and lower limits ofeach permeable stratum receiving iluid being established by the upperand lower limits of said anomalous constant temperature regions in saidinjection gradient, the incremental injection rates Q for eachincremental depth difference in each individual permeable stratum beingcalculated from:

(wherein Q1 Qn etc. are the incremental injection rates for successiveincremental thicknesses, l n in the permeable interval, Q0 is the totaltluid injection rate into all the permeable strata and is equal to theinjection rate into said well bore, A1 An are the incremental anomalousareas between the shut-in gradient and a pseudo expected shut-ingradient consisting of a line drawn parallel to said geothermal gradientand extending through the precise upper depth limit of the permeablestratum, said incremental anomalous areas also being bounded by theincremental depth differences for each incremental anomalous area 1 n,and 2A is the total of all the anomalous incremental areas A).

6. A method of determining the injection profile of an injectionborehole penetrating underground permeable strata which comprisescontinuing the flow of injection iluid through said injection boreholeat a steady rate, measuring the Variation in injection iluid temperatureTi with depth in said borehole to obtain an injection temperaturegradient at least through the permeable interval, shutting in theinjection borehole to terminate tluid flow therethrough, remeasuring atleast once the Variation in injection fluid` temperature Ts with depthof the stationary injection fluid present in said well bore to obtain atleast one shut-in temperature gradient, and then continuing theinjection iluid ilow; the upper extremity of each of said permeablestrata penetrated being precisely established at a depth h1 below whichTi remains substantially constant, the lower extremity of each of saidpermeable strata being precisely located at a depth h2 at the inflectionpoint below each constant temperature portion of said injectiontemperature gradient, an equivalent shut-in temperature gradients Tesbeing obtained by extrapolating said shut-in gradient through theanomalous temperature region thereof between depths h1 and h2, theincremental volumetric injection rates flowing into incrementalthicknesses of the permeable strata being obtained from the relation:

(wherein Q1 Qn etc. are the incremental volumetric injection rates intoeach incremental thicknesses 1 n in the permeable interval, Qn is thetotal volumetric injection fluid rate in the borehole, A1 An etc. areequal to the integral of T es-Ts as a function of depth between theincremental depth limits h1 and h2 for each incremental thickness ofeach permeable stratum, and 2A is the sum of all the integrals of Tes-Ts corresponding to all the permeable strata).

References Cited in the le of this patent UNITED STATES PATENTS2,050,128 Schlumberger Aug. 4, 1936 2,172,625 Schlumberger Sept. 12,1939 2,242,612 Leonardon May 20, 1941

5. A METHOD FOR DETERMINING THE INJECTION PORFILE OF A WELL BORE THROUGHWHICH INJECTION FLUIDS ARE PASSED INTO PERMEABLE UNDERGROUND. STRATAPENETRATED THEREBY WHICH COMPRISES DETERMINING THE GEOTHERMALTEMPERATURE GRADIENT THROUGH THE PERMEABLE INTERVAL, DETERMINING THEINJECTION TEMPERATURE GRADIENT WITHIN THE WELL BORE WHILE CONTINUING THEFLUID INJECTION, SHUTTING IN THE WELL FOR A PERIOD OF AT LEAST 10 HOURSTO TERMINATE ALL FLUID FLOW THEREIN, NEXT DETERMINING AT LEAST ONESHUT-IN TEPERATURE GRADIENT WITHIN SAID BORE IN THE ABSENCE OF FLUIDFLOW; SAID INJECTION AND SHUT-IN GRADIENTS BEING SEPARATELY DETERMINEDBY THE STEPS OF LOWERING A TEMPERATURE SENSITIVE DEVICE THROUGH THE WELLBORE TO A POINT ADJACENT THE PERMEABLE INTERVAL, SUSPENDING IT AT SAIDPOINT FOR AT LEAST 10 MINUTES TO ATTAIN THERMAL EQUILIBRIUM, THENPOSITIONING THE DEVICE SUCCESSIVELY AT A PLURALITY OF POINTS SEPARATEDBY INCREMENTAL DEPTH DIFFERENCES OPPOSITE THE PREMEABLE INTERVALPENETRATED BY SAID WELL BORE, RECORDING THE TEMPERATURE INDICATED ATEACH SUCCESSIVE DEPTH POINT AFTER HOLDING SAID DEVICE STATIONARY FOR ATLEAST 3 MINUTES AT EACH OF SAID POINTS, SAND CONTINUING THE INJECTIONFLUID FLOW INTO SAID WELL BORE; SAID INJECTION TEMPERATURE GRADIENTSHAVING ANOMALOUS REGIONS OF CONSTANT TEMPERATURE AND SAID SHUT-INGRADIENTS HAVING ANOMALOUS TEMPERATURE REGIONS THEREON CORRESPONDING TOTHE DEPTH OF EACH PERMEABLE STRATUM, THE PRECISE DEPTHS OF THE UPPER ANDLOWER LIMITS OF EACH PERMEABLE STRATUM RECEIVING FLUID BEING ESTABLISHEDBY THE UPPER AND LOWER LIMITS OF SAID NAOMALOUS CONSTANT TEMPERATUREREGIONS IN SAID INJECTION GRADIENT, THE INCREMENTAL INJECTION RATES QFOR EACH INCREMENTAL DEPTH DIFFERENCE IN EACH INDIVIDUAL PERMEABLESTRATUM BEING CALCULATED FROM: